The invention concerns a method for the selective removal and recovery of ammonia from gas mixtures containing ammonia and hydrogen sulfide.
With the coking of hard coal, pyrolysis gases form, which contain ammonia. The removal of the ammonia from the coking plant gas and its working up into ammonium sulfate according to the known indirect and half-direct methods contributed until about 1962 to the cost of coking. The then instituted degression of proceeds for valuable carbon materials in general, and for ammonia-containing products in particular, lead to introduction of methods for the destruction of the coking plant ammonia, in order to remove the ammonia from the coking plant gas, thus exclusively under the point of view of gas purification. Moreover, since in the presence of steam, hydrogen sulfide and hydrogen cyanide, ammonia acts strongly corrosively, it must be removed from the coking plant gas in order to protect gas distribution and working-up arrangements.
Considering increasing energy and raw material costs, and the thereby improved value of coking plant ammonia, it appears today no longer convenient to destroy the ammonia contained therein. It is, to the contrary, appropriate to recover the ammonia. This applies to all other gas mixtures, which--such as coking plant gas--contain among others, ammonia and hydrogen sulfide.
It has already been known for a long time that ammonia can be washed from coal distillation gases with an aqueous solution of ammonium bisulfite. Thus, at the beginning of this century, the Burkheiser method (DRP 212209, 215907, 217315) was run experimentally (See O. Grosskinsky, Handbook of Coking Plant Practice, Bd. II, Karl Knapp Verlag, Duesseldorf, 1958, pp. 286-287). Upon such washing, ammonium sulfite is formed which is oxidized into ammonium sulfate. The wash solution for this known method, however, does not selectively bind the ammonia, which enters instead into a side reaction with the hydrogen sulfide of the coal distillation gases, whereby there occurs a formation of sulphur dioxide in favor of a thio-sulfate concentration, whereby however the absorption capacity of the wash solution for ammonia is lowered.
The fundamental idea of the Burkheiser method is that there occurs a buildup of a greater solubility for the ammonium bisulfite compared to the ammonium sulfite, in such manner that crude coke oven gas, purged of sulfur, is washed with an ammonium bisulfite solution for absorption of the ammonia. The employed wash solution is again saturated with sulfurous acid, and returned into the circulation as wash liquid (Das Gas- und Wasserfach 70 (1927), pp. 309-310).